10 Gigabit Ethernet (10 GbE) is a set of Ethernet standards with a nominal data rate of 10 Gbit/s. 10 GbE over fiber, copper cabling and twisted pair are specified by the IEEE 802.3 standard. IEEE 802.3 is a collection of standards defining the physical layer, and the media access control (MAC) sublayer of the data link layer for wired Ethernet. IEEE 802.3ap, for example, provides a standard for Backplane Ethernet over printed circuit boards, with rates of 1 and 10 Gbit/s.
The IEEE 802.3ap standard defines the physical medium dependent sublayer (PMD) control function. The PMD control function implements the 10 GBASE-KR start-up protocol, which provides a mechanism through which the local receiver can tune the link-partner transmit equalizer to optimize performance over the backplane interconnect, and to inform the link partner when training is complete and it is ready to receive data. This mechanism is implemented through the continuous exchange of fixed-length training frames. These training frames are used by the two physical layer devices to exchange control and status information necessary to configure the adaptive equalization filters for both devices.
The training frames include long trails of ones and zeros (up to 16 ones and 16 zeros length). A Clock and Data Recovery (CDR) device, however, may not be able to maintain lock during these long trails of ones and zeros, potentially resulting in bit shifts in the recovered data. A need therefore exists for improved methods and apparatus for decoding such training frames.